Driving system for vehicle

ABSTRACT

A rotation speed of an electric oil pump in the case where an accelerator operation amount falls within a predetermined range is controlled to a rotation speed lower than the rotation speed of the electric oil pump in the case where the accelerator operation amount falls outside the predetermined range. When the range outside the predetermined range of the accelerator operation amount is set to a range in which noise that occurs from a source other than the electric oil pump is large, noise that occurs from the electric oil pump is masked by the noise that occurs from a source other than the electric oil pump and becomes inconspicuous in this range even when the rotation speed of the electric oil pump increases.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2016-028410 filed onFeb. 17, 2016 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to control over a driving system for avehicle, the driving system including an electric motor that serves as adriving source for propelling a vehicle and an electric oil pump thatsupplies oil to a cooling and lubrication required portion including theelectric motor.

2. Description of Related Art

There is known a driving system for a vehicle. The driving systemincludes an electric motor that serves as a vehicle driving source andan electric oil pump for supplying oil to a cooling and lubricationrequired portion including the electric motor. In the thus configureddriving system, the electric motor is cooled and a gear mechanism, andthe like, are lubricated by operating the electric oil pump in responseto a traveling state of a vehicle.

Incidentally, as the electric oil pump operates, noise due to theoperating sound of the electric oil pump occurs. As measures for noise,Japanese Patent Application Publication No. 2007-22296 (JP 2007-22296 A)describes that the operating range of an engine is controlled to a lowrotation and high torque (a range in which noise is large) in proportionto a vehicle speed. In the low rotation and high torque range of theengine, generally, thermal efficiency is high, while noise is large. Inresponse to this, since running noise increases as the vehicle speedincreases, noise of the engine becomes inconspicuous because of therunning noise, with the result that noise that is perceived by a driveris reduced. As described in JP 2007-22296 A, it is conceivable to makenoise from the electric oil pump inconspicuous by operating the electricoil pump such that noise from the electric oil pump is hidden by runningnoise that increases in proportion to the vehicle speed.

However, when noise is made inconspicuous by running noise duringtraveling as described in JP 2007-22296 A, it is difficult to make noisefrom the electric oil pump inconspicuous in a low vehicle speed range. Alubrication system, and the like, that require operation of the electricoil pump need to be operated even at a low vehicle speed. However, ifonly running noise of the vehicle is provided as means for making noisethat accompanies the operation of the electric oil pump inconspicuous,the operation of the electric oil pump is limited at a low vehiclespeed, so the amount of oil that is supplied to the cooling andlubrication required portion can be insufficient. Alternatively, whenthe electric oil pump is controlled such that the amount of oil that issupplied to the cooling and lubrication required portion is ensured,noise from the electric oil pump is conspicuous in the low vehicle speedrange.

SUMMARY

The present disclosure is contemplated against a backdrop of theabove-described situation, and provides a driving system for a vehicle,the driving system including an electric motor that serves as a vehicledriving source, an electric oil pump for supplying oil to a cooling andlubrication required portion including the electric motor, and acontroller that is able to ensure the amount of oil that is supplied bythe electric oil pump while noise that occurs from the electric oil pumpis made inconspicuous.

An aspect of the present disclosure provides a driving system for avehicle. The driving system includes an electric motor, an electric oilpump and an oil pump controller. The electric motor is configured tofunction as a driving source of the vehicle. The electric oil pump isconfigured to supply oil to a cooling and lubrication required portionincluding the electric motor. The oil pump controller is configured to(i) supply oil to the cooling and lubrication required portion bydriving the electric oil pump while the vehicle is traveling, and (ii)control a rotation speed of the electric oil pump when an acceleratoroperation amount of the vehicle falls within a predetermined range to arotation speed lower than a rotation speed of the electric oil pump whenthe accelerator operation amount falls outside the predetermined range.

The magnitude of noise due to the operating sound of the electric motorand inverter that controls the electric motor varies in response to theaccelerator operation amount. For example, when the acceleratoroperation amount is large and a required output of the electric motor islarge, or when regeneration control over the electric motor, which isexecuted in the case where the accelerator operation amount is zero orclose to zero, is being executed, a load on the electric motorincreases, so noise that occurs from the electric motor and the inverterincreases.

With the above-configured driving system, the rotation speed of theelectric oil pump in the case where the accelerator operation amountfalls within the predetermined range is controlled to a rotation speedlower than the rotation speed of the electric oil pump in the case wherethe accelerator operation amount falls outside the predetermined range.When the range outside the predetermined range of the acceleratoroperation amount is set to a range in which noise that occurs from asource other than the electric oil pump is large, noise that occurs fromthe electric oil pump is masked by the noise that occurs from a sourceother than the electric oil pump and becomes inconspicuous in this rangeeven when the rotation speed of the electric oil pump increases. Whenthe noise that occurs from a source other than the electric oil pump islarge, generally, a load on the electric motor also increases, so it isrequired to actively supply oil to the electric motor. In response tothis, since the electric oil pump is controlled at a high rotationspeed, oil is actively supplied to the electric motor, and the coolingability improves. On the other hand, when the range in which theaccelerator operation amount falls within the predetermined range is setto a range in which noise that occurs from a source other than theelectric oil pump is small, the rotation speed of the electric oil pumpdecreases, so, even when noise that occurs from a source other than theelectric oil pump is small, noise that occurs from the electric oil pumpalso reduces. As a result, it is possible to make the noise that occursfrom the electric oil pump inconspicuous. When noise that occurs from asource other than the electric oil pump is small, generally, a load onthe electric motor is also small, so the amount of oil required to coolthe electric motor also just needs to be small. Therefore, even when therotation speed of the electric oil pump decreases, shortage of theamount of supplied oil is prevented.

In the driving system, the oil pump controller may be configured to seta lower limit threshold of the predetermined range of the acceleratoroperation amount to a value at which regeneration control over theelectric motor is started.

With the thus configured driving system, the lower limit threshold ofthe predetermined range of the accelerator operation amount is set to avalue at which regeneration control over the electric motor is started.When the accelerator operation amount becomes smaller than or equal tothe lower limit threshold, regeneration control over the electric motoris started, and noise that occurs from the electric motor and theinverter increases. Therefore, it is possible to mask noise that occursfrom the electric oil pump by the noise that occurs from the electricmotor and the inverter and make the noise that occurs from the electricoil pump inconspicuous. That is, it is possible to drive the electricoil pump at a high rotation speed. During regeneration control over theelectric motor, a load on the electric motor increases and the electricmotor tends to generate heat. However, the electric oil pump is drivenat a high rotation speed, so it is possible to improve the coolingability by actively supply oil to the electric motor.

In the driving system, the oil pump controller may be configured to setthe lower limit threshold of the predetermined range to zero.

With the thus configured driving system, the lower limit threshold ofthe predetermined range of the accelerator operation amount is set tozero. When the accelerator operation amount becomes zero, regenerationcontrol over the electric motor is started, and noise that occurs fromthe electric motor and the inverter increases. Therefore, it is possibleto mask noise that occurs from the electric oil pump by the noise thatoccurs from the electric motor and the inverter and make the noise thatoccurs from the electric oil pump inconspicuous. That is, it is possibleto drive the electric oil pump at a high rotation speed. Duringregeneration control over the electric motor, a load on the electricmotor increases, and the electric motor tends to generate heat. However,since the electric oil pump is driven at a high rotation speed, it ispossible to improve the cooling ability by actively supplying oil to theelectric motor.

In the driving system, the oil pump controller may be configured tochange the rotation speed of the electric oil pump on the basis ofwhether a depression force on a brake pedal is larger than or equal to athreshold set in advance.

With the thus configured driving system, when the depression force onthe brake pedal is small, noise that occurs during regeneration controlover the electric motor is small; whereas, when the depression force onthe brake pedal increases, noise that occurs during regeneration controlincreases. For this reason, the threshold of the depression force on thebrake pedal, at which noise that occurs from the electric oil pumpbecomes inconspicuous because of noise that occurs during regenerationcontrol, is set, and the rotation speed of the electric oil pump ischanged on the basis of whether the depression force on the brake pedalis larger than or equal to the threshold. Thus, it is possible to drivethe electric oil pump at an appropriate rotation speed while maskingnoise from the electric oil pump by the noise that occurs duringregeneration control.

In the driving system, the oil pump controller may be configured tocontrol the rotation speed of the electric oil pump to zero, when theaccelerator operation amount falls within the predetermined range.

With the thus configured driving system, when the accelerator operationamount falls within the predetermined range, noise that occurs from theelectric motor and the inverter reduces. At this time, when the rotationspeed of the electric oil pump is controlled to zero, it is possible tocompletely eliminate noise that occurs from the electric oil pump.

In the driving system, the oil pump controller may be configured tocontrol the rotation speed of the electric oil pump to zero, when an oiltemperature of oil is higher than or equal to a predetermined oiltemperature.

With the thus configured driving system, when the oil temperature of oilis higher than or equal to the predetermined oil temperature, therotation speed of the electric oil pump is controlled to zero.Decreasing the rotation speed to zero further eliminates occurrence ofnoise from the electric oil pump, and provides a higher advantageouseffect. However, when the oil temperature is low and the viscosity ofoil is high, it takes time to supply oil to the cooling and lubricationrequired portion by driving the electric oil pump again after settingthe rotation speed of the electric oil pump to zero. For this reason,only in the case of the oil temperature at which it is possible toquickly supply oil to the cooling and lubrication required portion froma state where the rotation speed of the electric oil pump is zero, therotation speed of the electric oil pump is controlled to zero. Thus, itis possible to achieve both stable operation of the electric oil pumpand measures against noise.

In the driving system, the oil pump controller may be configured tocontrol the rotation speed of the electric oil pump in the case wherethe accelerator operation amount falls within the predetermined range toa rotation speed lower than the rotation speed of the electric oil pumpin the case where the accelerator operation amount falls outside thepredetermined range, when a vehicle speed becomes lower than or equal toa predetermined vehicle speed set in advance.

With the thus configured driving system, when the vehicle speed becomeslower than or equal to the predetermined vehicle speed, the rotationspeed of the electric oil pump in the case where the acceleratoroperation amount falls within the predetermined range is controlled to arotation speed lower than the rotation speed of the electric oil pump inthe case where the accelerator operation amount falls outside thepredetermined range. Therefore, even in a traveling state where runningnoise during traveling is small, it is possible to mask noise thatoccurs from the electric oil pump by noise that occurs from the electricmotor, the inverter, and the like, and make the noise that occurs fromthe electric oil pump inconspicuous.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the present disclosure will be described belowwith reference to the accompanying drawings, in which like numeralsdenote like elements, and wherein:

FIG. 1 is a skeletal view that illustrates the configuration of a hybridvehicle driving system according to embodiments of the presentdisclosure;

FIG. 2 is a view that illustrates a relevant portion of electricalsystem provided in order to control hybrid drive with the use of thevehicle driving system shown in FIG. 1;

FIG. 3 is a functional block diagram that illustrates a relevant portionof control functions provided in electronic control units shown in FIG.2;

FIG. 4 is a view that shows the relationship between an acceleratoroperation amount and a rotation speed of an electric oil pump and therelationship between an accelerator operation amount and a magnitude ofnoise in the vehicle driving system according to the first embodiment ofthe present disclosure;

FIG. 5 is a flowchart that illustrates control operations of acontroller over the electric oil pump in the vehicle driving systemaccording to the first embodiment of the present disclosure;

FIG. 6 is a flowchart that illustrates control operations of thecontroller over the electric oil pump in the vehicle driving systemaccording to the second embodiment of the present disclosure;

FIG. 7 is a view that shows the relationship between an oil temperatureand a target rotation speed of the electric oil pump in the case wherethe accelerator operation amount falls within a predetermined range inthe vehicle driving system according to the third embodiment of thepresent disclosure; and

FIG. 8 is a view that shows the relationship between an acceleratoroperation amount and a rotation speed of the electric oil pump in thevehicle driving system according to the fourth embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings. In the followingembodiments, the drawings are simplified or modified as needed, and thescale ratio, shape and the like, of each portion are not alwaysaccurately drawn.

FIG. 1 is a skeletal view that illustrates the configuration of a hybridvehicle driving system 10 (hereinafter, simply referred to as drivingsystem 10) that is part of a vehicle to which a first embodiment of thepresent disclosure is applied. The driving system 10 shown in FIG. 1 issuitably used in a front-engine front-drive (FF) vehicle. The drivingsystem 10 includes a first driving unit 16 and a second driving unit 18.The first driving unit 16 includes an engine 12 and a first electricmotor MG1. The engine 12 is a main driving force source. The seconddriving unit 18 includes a second electric motor MG2. The driving system10 transmits power, which is output from the first driving unit 16 orthe second driving unit 18, to a pair of right and left drive wheels 14r, 14 l (hereinafter, when not specifically distinguished from eachother, simply referred to as drive wheels 14) via a differential gearset 20 and a pair of right and left axles 22 r, 221 (hereinafter, whennot specifically distinguished from each other, simply referred to asaxles 22). The first electric motor MG1 and the second electric motorMG2 are examples of the electric motor according to the presentdisclosure.

The engine 12 is, for example, an internal combustion engine, such as agasoline engine and a diesel engine, which generates driving force as aresult of combustion of fuel that is directly injected into a cylinder.The first driving unit 16 includes a planetary gear train 24 and thefirst electric motor MG1. The planetary gear train 24 includes threerotating elements, that is, a sun gear S, a carrier CA and a ring gearR. The first electric motor MG1 is coupled to the sun gear S of theplanetary gear train 24. A one-way clutch F0 is provided between acrankshaft 26 and a housing (transaxle housing) 28. The crankshaft 26 isthe output shaft of the engine 12. The housing 28 is a non-rotatingmember. The one-way clutch F0 permits rotation of the engine 12 in theforward rotation direction, and prevents rotation of the engine 12 inthe reverse direction. Therefore, reverse rotation of the engine 12 isprevented by the one-way clutch F0.

The crankshaft 26 of the engine 12 is coupled to the carrier CA of theplanetary gear train 24. The carrier CA serves as an input rotatingmember of the first driving unit 16. The crankshaft 26 is coupled to amechanical oil pump 30. The ring gear R of the planetary gear train 24is coupled to a first output gear 32. The ring gear R serves as anoutput rotating member. The first output gear 32 is coupled to the drivewheels 14 via a large-diameter gear 36, a small-diameter gear 38, thedifferential gear set 20 and the axles 22 such that power istransmittable. The sun gear S of the planetary gear train 24 is coupledto the first electric motor MG1. That is, the planetary gear train 24 isan example of a differential mechanism including the carrier CA, the sungear S and the ring gear R. The carrier CA is coupled to the crankshaft26 of the engine 12, and is coupled to the one-way clutch F0. The sungear S is coupled to the first electric motor MG1. The ring gear R isthe output rotating member.

The first output gear 32 is in mesh with the large-diameter gear 36. Thelarge-diameter gear 36 is integrally provided with a counter shaft 34parallel to the crankshaft 26 of the first driving unit 16. Thesmall-diameter gear 38 integrally provided with the counter shaft 34 isin mesh with an input gear 40 of the differential gear set 20. Thelarge-diameter gear 36 is in mesh with a second output gear 44. Thesecond output gear 44 is coupled to an output shaft 42 of the secondelectric motor MG2. That is, the second electric motor MG2 is coupled tothe drive wheels 14 via the second output gear 44, the large-diametergear 36, the small-diameter gear 38, the differential gear set 20 andthe axles 22 such that power is transmittable. Each of the firstelectric motor MG1 and the second electric motor MG2 is a motorgenerator having the function of a motor that generates driving forceand the function of a generator that generates reaction force.

In the thus configured driving system 10, rotation output from theengine 12 in the first driving unit 16 is output from the first outputgear 32 via the planetary gear train 24 that serves as the differentialmechanism, and is input to the input gear 40 of the differential gearset 20 via the large-diameter gear 36 and the small-diameter gear 38that are provided on the counter shaft 34.

Rotation of the first electric motor MG1 in the first driving unit 16 istransmitted to the first output gear 32 via the planetary gear train 24,and is transmitted to the input gear 40 of the differential gear set 20via the large-diameter gear 36 and the small-diameter gear 38 that areprovided on the counter shaft 34. Rotation of the second electric motorMG2 in the second driving unit 18 is transmitted to the large-diametergear 36, which is provided on the counter shaft 34, via the output shaft42 and the second output gear 44, and is transmitted to the input gear40 of the differential gear set 20 via the large-diameter gear 36 andthe small-diameter gear 38. In the driving system 10 according to thefirst embodiment, each of the engine 12, the first electric motor MG1and the second electric motor MG2 is allowed to be used as a drivingsource for propelling the vehicle.

FIG. 2 is a view that illustrates a relevant portion of electricalsystem provided in order to control hybrid drive with the use of thedriving system 10. As shown in FIG. 2, the driving system 10, forexample, includes a hybrid drive control electronic control unit 50(HVECU or electronic control unit 50), an engine control electroniccontrol unit 52 (ENGECU or electronic control unit 52) and an electricmotor control electronic control unit 54 (MGECU or electronic controlunit 54). Each of these electronic control units 50, 52, 54 includes aso-called microcomputer. The microcomputer includes a CPU, a ROM, a RAM,input/output interfaces, and the like. The electronic control units 50,52, 54 execute various controls, such as hybrid drive control, with theuse of the engine 12, the first electric motor MG1 and the secondelectric motor MG2 by executing signal processing in accordance withprograms prestored in the ROM while utilizing a temporary storagefunction of the RAM. The electronic control unit 52 mainly executesdrive control over the engine 12. The electronic control unit 54 mainlyexecutes drive control over the first electric motor MG1 and the secondelectric motor MG2. The electronic control unit 50 executes drivecontrol, and the like, over the whole driving system 10 via theelectronic control units 52, 54. These electronic control units 50, 52,54 do not always need to be provided as individual control units, andmay be provided as an integral control unit. Each of the electroniccontrol units 50, 52, 54 may be further split into individual controlunits.

As shown in FIG. 2, various signals are supplied to the electroniccontrol unit 50 from various sensors, switches, and the like, providedat portions of the driving system 10. Specifically, a signal thatindicates a vehicle speed V, a signal that indicates an acceleratoroperation amount Acc, a signal that indicates a rotation speed Nmg1 ofthe first electric motor MG1, a signal that indicates a rotation speedNmg2 of the second electric motor MG2, a signal that indicates arotation speed Ne of the engine 12, a signal that indicates a state ofcharge SOC, a signal that indicates an input limit value Win and anoutput limit value Wout, a signal that indicates an oil temperatureToil, a signal that indicates a rotation speed Nop of an electric oilpump 75, a signal that indicates a stroke Bst (operation amount) of abrake pedal 73, and the like, are supplied to the electronic controlunit 50. The signal that indicates the vehicle speed V corresponds tothe rotation speed Nout of the first output gear 32, and is transmittedfrom a vehicle speed sensor 56. The signal that indicates theaccelerator operation amount Acc is the operation amount of anaccelerator pedal from an accelerator operation amount sensor 58. Theoperation amount of the accelerator pedal corresponds to a driver'srequired output amount. The signal that indicates the rotation speedNmg1 of the first electric motor MG1 is transmitted from an MG1 rotationspeed sensor 60. The signal that indicates the rotation speed Nmg2 ofthe second electric motor MG2 is transmitted from an MG2 rotation speedsensor 62. The signal that indicates the rotation speed Ne of the engine12 is transmitted from a crank angle sensor 64. The signal thatindicates the state of charge SOC is the amount of electric power storedin a battery (electrical storage device) (not shown), and is transmittedfrom a battery sensor 66. The signal that indicates the input limitvalue Win and the output limit value Wout is an input/output limit valuecommensurate with the state of charge SOC. The signal that indicates theoil temperature Toil is the temperature of oil for cooling andlubrication, and is transmitted from an oil temperature sensor 68. Theoil for cooling and lubrication is stored inside the driving system 10.The signal that indicates the rotation speed Nop of the electric oilpump 75 (described later) is transmitted from an EOP rotation speedsensor 69. The signal that indicates the stroke Bst (operation amount)of the brake pedal 73 is transmitted from a brake pedal stroke sensor71.

Command signals for executing drive control over the engine 12, drivecontrol over the first electric motor MG1 and drive control over thesecond electric motor MG2 are output from the electronic control unit 50to the electronic control units 52, 54. That is, for example, a drivingsignal to a throttle actuator, a fuel supply amount signal, an ignitionsignal, and the like, are output to the electronic control unit 52 as anengine torque command. The driving signal to the throttle actuator is asignal for controlling the output of the engine 12 via an engine outputcontrol device 70 (see FIG. 3). The driving signal is used to operatethe opening degree θth of an electronic throttle valve provided in anintake pipe of the engine 12. The fuel supply amount signal is used tocontrol a fuel supply amount to the intake pipe, or the like, from afuel injection device. The ignition signal provides an ignition devicewith a command on the ignition timing of the engine 12. A command signalfor controlling electric energy that is supplied to the first electricmotor MG1 is output to the electronic control unit 54 as an MG1 torquecommand. A command signal for controlling electric energy that issupplied to the second electric motor MG2 is output to the electroniccontrol unit 54 as an MG2 torque command. The electric energy issupplied from the battery (not shown) to the first electric motor MG1via a first inverter 72 (see FIG. 3), and the electric energy issupplied from the battery (not shown) to the second electric motor MG2via a second inverter 74 (see FIG. 3). A driving current as a command todrive the electric oil pump 75 is output from the electronic controlunit 50.

FIG. 3 is a functional block diagram that illustrates a relevant portionof control functions provided in the electronic control units 50, 52,54, and the like. A hybrid drive control unit 76 shown in FIG. 3 isfunctionally provided in the electronic control unit 50. These controlfunctions may be provided in any one of the electronic control units 50,52, 54. An engine drive control unit 78 included in the hybrid drivecontrol unit 76 may be functionally provided in the electronic controlunit 52. A first electric motor drive control unit 80 and a secondelectric motor drive control unit 82 are functionally provided in theelectronic control unit 54. The hybrid drive control unit 76, the enginedrive control unit 78, the first electric motor drive control unit 80and the second electric motor drive control unit 82 may executeprocessing by transmitting and receiving information among theelectronic control units 50, 52, 54.

The hybrid drive control unit 76 shown in FIG. 3 executes hybrid drivecontrol over the driving system 10. Specifically, the hybrid drivecontrol unit 76 controls the driving of the engine 12 via the engineoutput control device 70, and controls driving (motoring) or powergeneration (regeneration) of each of the first electric motor MG1 andthe second electric motor MG2 via a corresponding one of the firstinverter 72 and the second inverter 74. In order to execute suchcontrol, the hybrid drive control unit 76 includes the engine drivecontrol unit 78, the first electric motor drive control unit 80, thesecond electric motor drive control unit 82 and an EOP drive controlunit 84. The EOP drive control unit 84 is an example of the oil pumpcontroller according to the present disclosure.

The engine drive control unit 78 controls the driving of the engine 12via the engine output control device 70. Specifically, the drivingsignal to the throttle actuator, the fuel supply amount signal, theignition signal, and the like, are supplied to the engine output controldevice 70 via the electronic control unit 52 such that the output of theengine 12 becomes a target engine output (a target rotation speed and atarget output torque) that is calculated by the electronic control unit50. The driving signal is a signal that is used to operate the openingdegree θth of the electronic throttle valve provided in the intake pipeof the engine 12. The fuel supply amount signal is a signal that is usedto control the fuel supply amount to the intake pipe, or the like, fromthe fuel injection device. The ignition signal is a signal that providesthe ignition device with a command on the ignition timing of the engine12.

The first electric motor drive control unit 80 controls the operation ofthe first electric motor MG1 via the first inverter 72. Specifically,the first electric motor drive control unit 80 supplies a signal to thefirst inverter 72 via the electronic control unit 54 such that theoutput of the first electric motor MG1 becomes a target first electricmotor output (a target rotation speed and a target output torque). Thesignal is used to control the input and output of electric energybetween the battery (not shown) and the first electric motor MG1. Thetarget first electric motor output is calculated by the electroniccontrol unit 50.

The second electric motor drive control unit 82 controls the operationof the second electric motor MG2 via the second inverter 74.Specifically, the second electric motor drive control unit 82 supplies asignal to the second inverter 74 via the electronic control unit 54 suchthat the output of the second electric motor MG2 becomes a target secondelectric motor output (a target rotation speed and a target outputtorque). The signal is used to control the input and output of electricenergy between the battery (not shown) and the second electric motorMG2. The target second electric motor output is calculated by theelectronic control unit 50.

The hybrid drive control unit 76 executes hybrid drive control with theuse of the driving system 10 via the engine drive control unit 78, thefirst electric motor drive control unit 80 and the second electric motordrive control unit 82. For example, the hybrid drive control unit 76calculates a required driving force Treq (required driving torque) onthe basis of the accelerator operation amount Acc, the vehicle speed V,and the like, by consulting a map (not shown) stored in a predeterminedstorage device, and causes at least one of the engine 12, the firstelectric motor MG1 and the second electric motor MG2 to generate arequired output such that the vehicle drives with a small amount ofexhaust gas emission at a low fuel consumption in response to thecalculated required driving force Treq. The accelerator operation amountAcc is detected by the accelerator operation amount sensor 58. Thevehicle speed V is detected by the vehicle speed sensor 56. The requireddriving force Treq (required driving torque) is a target value ofdriving force (driving torque) to be transmitted to the drive wheels 14.For example, a motor drive mode (EV mode), an engine drive mode, ahybrid drive mode, or the like, is selectively established in responseto the traveling state of the vehicle. The motor drive mode (EV mode) isa mode in which the engine 12 is stopped and the vehicle travels byusing at least one of the first electric motor MG1 and the secondelectric motor MG2 as a driving source. The engine drive mode is a modein which only the engine 12 is used as a driving source and the vehicletravels by mechanically transmitting the power of the engine 12 to thedrive wheels 14. The hybrid drive mode is a mode in which the vehicletravels by using both the engine 12 and the second electric motor MG2(or the first electric motor MG1 in addition to both the engine 12 andthe second electric motor MG2) as driving sources.

The hybrid drive control unit 76 suitably executes control for changingthe drive mode among the motor drive mode, the engine drive mode and thehybrid drive mode. The motor drive mode is a drive mode in which theengine 12 is stopped. The engine drive mode and the hybrid drive modeare drive modes in which the engine 12 is driven. For example, when thestate of charge SOC of the battery (not shown) is higher than apredetermined threshold Sbo, the motor drive mode, which is the drivemode in which the engine 12 is stopped, is established. On the otherhand, when the state of charge SOC is lower than or equal to thethreshold Sbo, the engine drive mode or the hybrid drive mode, which isthe drive mode in which the engine 12 is driven, is established. Controlfor changing the drive mode is executed on the basis of the acceleratoroperation amount Acc that is detected by the accelerator operationamount sensor 58, the vehicle speed V that is detected by the vehiclespeed sensor 56, and the like.

The operation of the driving system 10 in the motor drive mode will bedescribed. In the motor drive mode, the engine 12 is not driven, and therotation speed of the engine 12 is set to zero. Specifically, rotationof the crankshaft 26 in the reverse direction is prevented by theone-way clutch F0 that functions as a lock mechanism, and rotation ofthe crankshaft 26 is set to a non-rotating state. In this state, themotoring torque of the second electric motor MG2 is transmitted to thedrive wheels 14 as a driving force in a vehicle forward travelingdirection. The motoring torque of the first electric motor MG1 istransmitted to the drive wheels 14 as a driving force in the vehicleforward traveling direction. That is, the rotation speed of the ringgear R that is an example of the output rotating member is increased inthe forward rotation direction by using the motoring torque of the firstelectric motor MG1. In the driving system 10, the crankshaft 26 of theengine 12 is locked (fixed) by the one-way clutch F0 in zero rotation,so it is possible to use the first electric motor MG1 and the secondelectric motor MG2 as driving sources for propelling the vehicletogether.

The operation of the driving system 10 in the engine drive mode or inthe hybrid drive mode will be described. In the engine drive mode or inthe hybrid drive mode, when reaction torque generated by the firstelectric motor MG1 is input to the sun gear S against the output torqueof the engine 12, which is input to the carrier CA, the first electricmotor MG1 is caused to function as a generator. When the rotation speed(output shaft rotation speed) of the ring gear R is constant, therotation speed Ne of the engine 12 is allowed to be continuously(steplessly) varied by increasing or decreasing the rotation speed ofthe first electric motor MG1. That is, it is possible to execute controlfor setting the rotation speed Ne of the engine 12 to, for example, arotation speed at which fuel efficiency is the highest through motoringcontrol and reaction control over the first electric motor MG1. A hybridsystem of this type is referred to as a mechanical distribution type ora split type.

As the drive mode is changed into the motor drive mode as a request tooperate the electric oil pump 75, the EOP drive control unit 84 drivesthe electric oil pump 75 as needed. Oil pumped by the electric oil pump75 is supplied via oil passages (not shown) to portions that need to becooled and lubricated, such as the first electric motor MG1, the secondelectric motor MG2 (hereinafter, when not specifically distinguishedfrom each other, referred to as electric motors MG) and the planetarygear train 24. That is, the electric oil pump 75 functions as an oilsupply device for supplying oil to the electric motors MG the planetarygear train 24, and the like, while the vehicle is traveling. The firstelectric motor MG1, the second electric motor MG2, and various meshinggears including the planetary gear train 24, are examples of the coolingand lubrication required portion according to the present disclosure.

The EOP drive control unit 84 stops the electric oil pump 75 while thevehicle is traveling in the engine drive mode or the hybrid drive mode,in which the engine 12 is driven. This is because, in the engine drivemode or the hybrid drive mode, the mechanical oil pump 30 is driven asthe engine 12 is driven and oil pumped by the mechanical oil pump 30 issupplied to the electric motors MG the planetary gear train 24, and thelike, via the oil passages (not shown).

When the drive mode is changed into the motor drive mode, the EOP drivecontrol unit 84 calculates a target rotation speed Nop* of the electricoil pump 75, and controls the driving current to the electric oil pump75 such that the electric oil pump 75 is driven to rotate at the targetrotation speed Nop*. The EOP drive control unit 84, for example, detectsthe rotation speed Nop of the electric oil pump 75 whenever necessary,and executes rotation speed control such that the actual rotation speedNop follows the target rotation speed Nop*.

The EOP drive control unit 84 calculates the target rotation speed Nop*on the basis of the vehicle speed V, the accelerator operation amountAcc and the oil temperature Toil. The EOP drive control unit 84determines whether the vehicle speed V is lower than or equal to apredetermined vehicle speed V1 set in advance.

As the vehicle speed V increases, running noise increases. Therefore,even when the electric oil pump 75 is driven to rotate at a highrotation speed, noise due to the operating sound of the electric oilpump 75 is smaller than the running noise, so the noise is masked by therunning noise and becomes inconspicuous. The EOP drive control unit 84determines whether the vehicle speed V is lower than or equal to thepredetermined vehicle speed V1 set in advance. When the vehicle speed Vexceeds the predetermined vehicle speed V1, the EOP drive control unit84 sets the target rotation speed Nop* to a rotation speed A set inadvance.

The predetermined vehicle speed V1 of the vehicle speed V is empiricallyor analytically obtained in advance. The predetermined vehicle speed V1of the vehicle speed V is set to a value at which noise that occurs atthe time when the electric oil pump 75 is driven to rotate at therotation speed A is masked by the running noise and becomesinconspicuous while the vehicle is traveling. The rotation speed A ofthe electric oil pump 75 is also empirically or analytically obtained inadvance. The rotation speed A of the electric oil pump 75 is set to arotation speed at which it is possible to supply the amount of oil thatis required to cool the electric motors MG and lubricate the variousmeshing gears.

On the other hand, when the vehicle speed V falls within a range lowerthan or equal to the predetermined vehicle speed V1, the EOP drivecontrol unit 84 determines the target rotation speed Nop* on the basisof the relationship (described later) obtained and stored in advance andshown in FIG. 4, and controls the electric oil pump 75 such that therotation speed Nop of the electric oil pump 75 becomes the targetrotation speed Nop*. The upper graph in FIG. 4 shows the relationshipbetween an accelerator operation amount Acc and a rotation speed Nop ofthe electric oil pump 75. The abscissa axis represents the acceleratoroperation amount Acc. The ordinate axis represents the rotation speedNop of the electric oil pump 75. The continuous line indicates theactual rotation speed Nop of the electric oil pump 75. The alternatelong and short dashes line indicates the target rotation speed Nop*. Asshown in FIG. 4, in the first embodiment, in the range in which thevehicle speed V is lower than or equal to the predetermined vehiclespeed V1, the rotation speed Nop of the electric oil pump 75 is changedon the basis of the accelerator operation amount Acc.

As shown in FIG. 4, in the low vehicle speed range in which the vehiclespeed V is lower than or equal to the predetermined vehicle speed V1,the target rotation speed Nop* is determined on the basis of theaccelerator operation amount Acc. The target rotation speed Nop*indicated by the alternate long and short dashes line in the case wherethe accelerator operation amount Acc falls within the range from apredetermined value X to a predetermined value Y is set to a lower valuethan the target rotation speed Nop* in the case where the acceleratoroperation amount Acc falls within the range smaller than thepredetermined value X or the range larger than the predetermined valueY. Therefore, the EOP drive control unit 84 controls the rotation speedNop of the electric oil pump 75 in the case where the acceleratoroperation amount Acc falls within the range from the predetermined valueX to the predetermined value Y to a rotation speed lower than therotation speed Nop in the case where the accelerator operation amountAcc falls outside the range. The range of the accelerator operationamount Acc from the predetermined value X to the predetermined value Yis an example of the predetermined range according to the presentdisclosure.

As shown in FIG. 4, in the case where the accelerator operation amountAcc falls within the range from the predetermined value X to thepredetermined value Y, the target rotation speed Nop* is set to arotation speed B indicated by the alternate long and short dashes line.In the case where the accelerator operation amount Acc falls within therange larger than zero and smaller than the predetermined value X, thetarget rotation speed Nop* is set to a rotation speed C indicated by thealternate long and short dashes line and higher than the rotation speedB. Accordingly, the actual rotation speed Nop of the electric oil pump75, indicated by the continuous line, steep decreases so as to followthe target rotation speed Nop*. The rotation speed C that is set in thecase where the accelerator operation amount Acc is smaller than thepredetermined value X corresponds to the case where a depression forceBS on the brake pedal 73 exceeds a threshold F set in advance. Thethreshold F of the depression force BS on the brake pedal 73 will bedescribed later. The depression force BS on the brake pedal 73 iscalculated on the basis of a variation per unit time in the stroke Bstof the brake pedal 73. The stroke Bst is detected by the brake pedalstroke sensor. Alternatively, it is also possible to calculate thedepression force BS on the brake pedal 73 on the basis of a hydraulicpressure applied to a hydraulic cylinder that is operatively coupled tothe brake pedal 73.

The rotation speed B is empirically or analytically obtained in advance.In a traveling state where the accelerator operation amount Acc fallswithin the range from the predetermined value X to the predeterminedvalue Y, the rotation speed B is set to a rotation speed at which it ispossible to supply the amount of oil required from the electric motorsMG and the like, within the range in which noise that occurs from theelectric oil pump 75 is masked by noise that occurs from sources otherthan the electric oil pump 75 and becomes inconspicuous. The noise thatoccurs from sources other than the electric oil pump 75 includes noisedue to the operating sound of the first electric motor MG1, firstinverter 72, second electric motor MG2, second inverter 74, and thelike, and noise that occurs from the meshing gears including theplanetary gear train 24. The rotation speed C is also empirically oranalytically obtained in advance. The rotation speed C is set to arotation speed at which it is possible to supply the amount of oilrequired against heat generation due to regeneration control over thesecond electric motor MG2 within the range in which noise that occursfrom the electric oil pump 75 is masked by noise that occurs fromsources other than the electric oil pump 75, including noise due toregeneration control over the second electric motor MG2 and becomesinconspicuous.

In the case where the accelerator operation amount Acc is larger thanzero and smaller than the predetermined value X, the brake pedal 73 canbe depressed, and the amount of regeneration of the second electricmotor MG2 varies depending on the depression force BS of the brake pedal73. For example, when the brake pedal 73 is not depressed or depressedlightly, that is, when the depression force BS on the brake pedal 73 issmall, the amount of regeneration during regeneration control is small,so noise that occurs from the second electric motor MG2 and the secondinverter 74 is small. On the other hand, when the brake pedal 73 isdepressed strongly, that is, when the depression force BS on the brakepedal 73 is large, the amount of regeneration during regenerationcontrol is large, so noise that occurs from the second electric motorMG2 and the second inverter 74 is large.

In consideration of the above, in the first embodiment, the threshold Fof the depression force BS on the brake pedal 73 is set, and, when thedepression force BS is larger than or equal to the threshold F, thetarget rotation speed Nop* of the electric oil pump 75 is set to therotation speed C. When the depression force BS on the brake pedal 73 issmaller than the threshold F, the target rotation speed Nop* of theelectric oil pump 75 is changed between the rotation speed B and therotation speed C in response to the depression force BS on the brakepedal 73. Specifically, as the depression force BS on the brake pedal 73increases, the target rotation speed Nop* is set to a larger value (themaximum value is the rotation speed C). The threshold F of thedepression force BS on the brake pedal 73 is empirically or analyticallyobtained in advance. The threshold F is set to a value at whichregeneration noise during regeneration control is sufficiently large andnoise from the electric oil pump 75 is masked by the regeneration noiseand becomes inconspicuous.

The predetermined value X is set to a value close to zero. Specifically,the predetermined value X is set to a value at which the second electricmotor MG2 is changed from drive control to regeneration control (a valueat which regeneration control is started). When regeneration controlover the second electric motor MG2 is executed, regeneration noise dueto regeneration control occurs from the second electric motor MG2. Sincethis noise is sufficiently larger than noise that occurs from theelectric oil pump 75, even when the rotation speed of the electric oilpump 75 increases, the noise that occurs from the electric oil pump 75is masked by the regeneration noise that occurs from the second electricmotor MG2. When regeneration control is set to start in the case wherethe accelerator operation amount Acc is zero, the predetermined value Xmay be zero. The predetermined value X is an example of the lower limitthreshold of the predetermined range according to the presentdisclosure.

In the case where the accelerator operation amount Acc exceeds thepredetermined value Y, the target rotation speed Nop* of the electricoil pump 75 is set to a rotation speed indicated by the alternate longand short dashes line and higher than the rotation speed B. The actualrotation speed Nop of the electric oil pump 75, indicated by thecontinuous line, steeply increases so as to follow the target rotationspeed Nop*. In a high load range of the electric motors MG in which theaccelerator operation amount Acc exceeds the predetermined value Y, therotation speed Nop is allowed to vary as indicated by the continuousline in FIG. 4 as a result of further executing rotation speed controlbased on the accelerator operation amount Acc, the vehicle speed V, andthe like. The case where the accelerator operation amount Acc exceedsthe predetermined value Y in the case where the vehicle speed V is lowerthan the predetermined vehicle speed V1 corresponds to, for example, acase where the vehicle is traveling on an uphill road, or the like.

The predetermined value Y is, for example, set to a point at which thedriving of the first electric motor MG1 is started in addition to thedriving of the second electric motor MG2. In the motor drive mode,basically, the vehicle is caused to travel by using the driving force ofthe second electric motor MG2; however, when the required driving forceTreq is large, motoring torque is also output from the first electricmotor MG1. At this time, noise also occurs from the first electric motorMG1 and the first inverter 72. Therefore, when the accelerator operationamount Acc exceeds the predetermined value Y, noise also occurs from thefirst electric motor MG1, so noise steeply increases. At this time, evenwhen the electric oil pump 75 operates in a situation that the rotationspeed Nop of the electric oil pump 75 is the rotation speed A higherthan the rotation speed B, noise that occurs from the electric oil pump75 is masked by noise that occurs from sources other than the electricoil pump 75, including noise from the first electric motor MG1, andbecomes inconspicuous. The rotation speed A of the electric oil pump 75is empirically obtained in advance. The rotation speed A is set to arotation speed at which the amount of oil required is supplied to theelectric motors MG, the planetary gear train 24, and the like, withinthe range in which noise that occurs from the electric oil pump 75 ismasked by noise that occurs from sources other than the electric oilpump 75, including the first electric motor MG1 and the second electricmotor MG2.

The lower graph in FIG. 4 shows a magnitude (NV level) of noise thatoccurs from the electric oil pump 75 (EOP) (hereinafter, EOP noise) anda magnitude of noise that occurs from sources other than the electricoil pump 75 (other than the EOP) (hereinafter, non-EOP noise). In FIG.4, the dashed line indicates non-EOP noise, and the continuous lineindicates EOP noise. The non-EOP noise in the lower graph of FIG. 4, forexample, includes noise that occurs from the electric motors MG, noisethat occurs from the inverters 72, 74, noise that occurs from themeshing gears that constitute the planetary gear train 24, and the like.The non-EOP noise does not include noise from the engine 12 since noiseis measured in the motor drive mode in which the engine 12 is stopped.

As shown in FIG. 4, in the case where the accelerator operation amountAcc is larger than zero and smaller than the predetermined value X,non-EOP noise is large because of occurrence of noise due toregeneration control over the second electric motor MG2. In addition tothis, EOP noise also increases as a result of an increase in therotation speed of the electric oil pump 75; however, the EOP noise issufficiently smaller than the non-EOP noise, so the noise that occursfrom the electric oil pump 75 is masked by the non-EOP noise and becomesinconspicuous. Therefore, the driver does not experience a feeling ofstrangeness due to the noise from the electric oil pump 75. The amountof heat generation of the second electric motor MG2 also increases as aresult of regeneration control over the second electric motor MG2. Inresponse to this, the amount of oil supplied to the electric motors MGincreases since the rotation speed Nop of the electric oil pump 75 isincreased, so the ability to cool the electric motors MG improves.

In the case where the accelerator operation amount Acc falls within therange from the predetermined value X to the predetermined value Y, thesecond electric motor MG2 changes into a motoring side, and theaccelerator operation amount Acc is also relatively small, so a load onthe second electric motor MG2 is also small. Therefore, non-EOP noisereduces. In addition to this, since the electric oil pump 75 rotates ata low rotation speed (rotation speed B), noise that occurs from theelectric oil pump 75 also reduces. Therefore, in the case where theaccelerator operation amount Acc falls within the range from thepredetermined value X to the predetermined value Y as well, EOP noise ismasked by non-EOP noise and becomes inconspicuous, so the driver doesnot experience a feeling of strangeness due to the noise from theelectric oil pump 75. Since the accelerator operation amount Acc isrelatively small, a load on the second electric motor MG2 also reduces,so the amount of heat generation of the second electric motor MG2 alsoreduces. As a result, the amount of oil required to, for example, coolthe second electric motor MG2 is also small. Therefore, the rotationspeed Nop of the electric oil pump 75 may be low.

In the case where the accelerator operation amount Acc exceeds thepredetermined value Y, since motoring torque is also output from thefirst electric motor MG1 in addition to motoring torque that is outputfrom the second electric motor MG2, so non-EOP noise increases. Inaddition to this, EOP noise increases as a result of an increase in therotation speed Nop of the electric oil pump 75; however, the EOP noiseis sufficiently smaller than the non-EOP noise, so the EOP noise ismasked by the non-EOP noise and becomes inconspicuous. Therefore, thedriver does not experience a feeling of strangeness due to the noisefrom the electric oil pump 75. When the accelerator operation amount Accexceeds the predetermined value Y, not only the second electric motorMG2 but also the first electric motor MG1 generates heat, so the amountof oil required to cool the electric motors MG increases. However, sincethe rotation speed Nop of the electric oil pump 75 is increased, theamount of oil supplied to the electric motors MG increases, so theability to cool the electric motors MG improves. As a result, heatgeneration of the electric motors MG is reduced, so it is also possibleto further extend a driving time of the first electric motor MG1 andsecond electric motor MG2.

In this way, the rotation speed of the electric oil pump 75 is changedin response to not only the vehicle speed V but also the acceleratoroperation amount Acc, so noise that occurs from the electric oil pump 75is masked by noise that occurs from mainly the electric motors MG andbecomes inconspicuous. As a result, the driver does not experience afeeling of strangeness due to the noise that occurs from the electricoil pump 75. In addition, the rotation speed Nop of the electric oilpump 75 is optimally controlled in response to the accelerator operationamount Acc, so shortage of oil supplied to the electric motors MG, andthe like, is also prevented.

FIG. 5 is a flowchart that illustrates control operations of theelectronic control units 50, 52, 54 and, specifically, controloperations over the electric oil pump 75. This flowchart is repeatedlyexecuted while the vehicle is traveling.

Initially, in step S1 (hereinafter, step is omitted) corresponding tothe function of the EOP drive control unit 84, it is determined whethera request to operate the electric oil pump 75 has been output. A requestto operate the electric oil pump 75 is, for example, output when thedrive mode has been changed into the motor drive mode. When a request tooperate the electric oil pump 75 has not been output, negativedetermination is made in S1, and the process proceeds to S6. In S6corresponding to the function of the EOP drive control unit 84, theelectric oil pump 75 is stopped in the case where the electric oil pump75 is operating. When the electric oil pump 75 has been already stopped,the process returns. When a request to operate the electric oil pump 75has been output, affirmative determination is made in S1, and theprocess proceeds to S2.

In S2 corresponding to the function of the EOP drive control unit 84, itis determined whether the vehicle speed V is lower than or equal to thepredetermined vehicle speed V1. When the vehicle speed V exceeds thepredetermined vehicle speed V1, negative determination is made in S2,and the process proceeds to S5. When the vehicle speed V is lower thanor equal to the predetermined vehicle speed V1, affirmativedetermination is made in S2, and the process proceeds to S3.

In S3 corresponding to the function of the EOP drive control unit 84, itis determined whether the accelerator operation amount Acc falls withinthe range from the predetermined value X to the predetermined value Y.When the accelerator operation amount Acc falls within the range fromthe predetermined value X to the predetermined value Y, affirmativedetermination is made in S3, and the process proceeds to S7. In S7corresponding to the function of the EOP drive control unit 84, it isdetermined that noise that occurs from sources other than the electricoil pump 75 (non-EOP noise) is small, the target rotation speed Nop* ofthe electric oil pump 75 is set to the rotation speed B, and theelectric oil pump 75 is controlled so as to operate at the rotationspeed B. Thus, non-EOP noise reduces; however, noise that occurs fromthe electric oil pump 75 (EOP noise) also reduces, so the EOP noise isinconspicuous.

Referring back to S3, when the accelerator operation amount Acc fallsoutside the range from the predetermined value X to the predeterminedvalue Y, the process proceeds to S4. In S4 corresponding to the functionof the EOP drive control unit 84, it is determined whether theaccelerator operation amount Acc is smaller than the predetermined valueX. When the accelerator operation amount Acc is smaller than thepredetermined value X, affirmative determination is made in S4, and theprocess proceeds to S8.

In S8 corresponding to the function of the EOP drive control unit 84, itis determined whether the depression force BS on the brake pedal 73 islarger than or equal to the threshold F set in advance. When thedepression force BS on the brake pedal 73 is larger than or equal to thethreshold F, affirmative determination is made in S8, and the processproceeds to S9. In S9 corresponding to the function of the EOP drivecontrol unit 84, the target rotation speed Nop* of the electric oil pump75 is set to the rotation speed C, and the electric oil pump 75 iscontrolled so as to operate at the rotation speed C. When the depressionforce BS on the brake pedal 73 is smaller than the threshold F in S8,negative determination is made in S8, and the process proceeds to S10.In S10 corresponding to the function of the EOP drive control unit 84,the target rotation speed Nop* of the electric oil pump 75 is set to avalue between the rotation speed B and the rotation speed C in responseto the depression force BS on the brake pedal 73, and the electric oilpump 75 is controlled so as to operate at the set rotation speed. In thecase where the accelerator operation amount Acc is smaller than thepredetermined value X, regeneration control over the second electricmotor MG2 is executed, noise that occurs from the second electric motorMG2 (regeneration noise) increases, so EOP noise tends to be masked bynoise from the second electric motor MG2, and the like. Therefore, whenthe electric oil pump 75 is controlled at the rotation speed between therotation speed B and the rotation speed C as well, the EOP noise ismasked by the non-EOP noise and becomes inconspicuous. Since theelectric oil pump 75 is driven at the rotation speed higher than therotation speed B, the amount of supplied oil increases against heatgeneration due to regeneration control over the second electric motorMG2, so the cooling ability improves.

Referring back to S4, when the accelerator operation amount Acc exceedsthe predetermined value Y, negative determination is made in S4, and theprocess proceeds to S5. In S5 corresponding to the function of the EOPdrive control unit 84, the target rotation speed Nop* of the electricoil pump 75 is set to the rotation speed A, and the electric oil pump 75is controlled so as to be driven at the rotation speed A. When theaccelerator operation amount Acc exceeds the predetermined value Y, notonly the second electric motor MG2 but also the first electric motor MG1outputs motoring torque, so noise that occurs from the electric motorsMG increases. Thus, even when the electric oil pump 75 is controlled atthe rotation speed A higher than the rotation speed B, EOP noise ismasked by non-EOP noise and becomes inconspicuous. When negativedetermination is made in S2 as well, the electric oil pump 75 iscontrolled in S5 so as to operate at the rotation speed A. When negativedetermination is made in S2, the vehicle speed V is higher than thepredetermined vehicle speed V1, and running noise is large, so EOP noiseis masked by the running noise and becomes inconspicuous. Since theelectric oil pump 75 is driven at the rotation speed A, the amount ofoil supplied to the electric motors MG and the like, also increases.

As described above, according to the first embodiment, the rotationspeed Nop of the electric oil pump 75 in the case where the acceleratoroperation amount Acc falls within the range from the predetermined valueX to the predetermined value Y is controlled to a rotation speed lowerthan the rotation speed Nop of the electric oil pump 75 in the casewhere the accelerator operation amount Acc falls outside the range fromthe predetermined value X to the predetermined value Y. In the casewhere the accelerator operation amount Acc falls outside the range fromthe predetermined value X to the predetermined value Y, the rotationspeed Nop of the electric oil pump 75 is high, so noise that occurs fromthe electric oil pump 75 also increases. In the case where theaccelerator operation amount Acc falls outside the range from thepredetermined value X to the predetermined value Y, noise from sourcesother than the electric oil pump 75 is large, so noise from the electricoil pump 75 is masked by the noise from sources other than the electricoil pump 75 and becomes inconspicuous. In the case where the acceleratoroperation amount Acc falls outside the range from the predeterminedvalue X to the predetermined value Y, a load on the electric motors MGalso increases, so oil needs to be actively supplied to the electricmotors MG. However, since the electric oil pump 75 is controlled at arotation speed higher than the rotation speed that is used in the casewhere the accelerator operation amount Acc falls within the range fromthe predetermined value X to the predetermined value Y, oil is activelysupplied to the electric motors MG so the cooling ability improves. Onthe other hand, in the case where the accelerator operation amount Accfalls within the range from the predetermined value X to thepredetermined value Y, the rotation speed Nop of the electric oil pump75 decreases, so noise from the electric oil pump 75 also reduces. Inthe case where the accelerator operation amount Acc falls within therange from the predetermined value X to the predetermined value Y, aload on the electric motors MG also reduces. Therefore, even when therotation speed Nop of the electric oil pump 75 decreases, the amount ofoil required to cool the electric motors MG reduces, so shortage of oilsupplied is also prevented.

According to the first embodiment, when the accelerator operation amountAcc is smaller than the predetermined value X, regeneration control overthe second electric motor MG2 is started, so noise that occurs from thesecond electric motor MG2 and the second inverter 74 increases.Therefore, it is possible to mask noise from the electric oil pump 75 bynoise from sources other than the electric oil pump 75 and make thenoise from the electric oil pump 75 inconspicuous. Therefore, it ispossible to drive the electric oil pump 75 at a high rotation speed.During regeneration control over the second electric motor MG2, a loadon the second electric motor MG2 increases, and heat tends to begenerated. However, when the electric oil pump 75 is driven at the highrotation speed Nop, it is possible to actively supply oil to the secondelectric motor MG2 and improve the cooling ability.

According to the first embodiment, when the depression force BS on thebrake pedal 73 is small, noise that occurs during regeneration controlover the electric motor is small; whereas, when the depression force BSon the brake pedal 73 increases, noise that occurs during regenerationcontrol increases. For this reason, the threshold F of the depressionforce BS on the brake pedal 73, at which noise that occurs from theelectric oil pump 75 becomes inconspicuous because of noise that occursduring regeneration control, is set, and the target rotation speed Nop*of the electric oil pump 75 is changed on the basis of whether thedepression force BS on the brake pedal 73 is larger than or equal to thethreshold F. Thus, it is possible to drive the electric oil pump 75 atan appropriate rotation speed while masking noise from the electric oilpump 75 by noise that occurs during regeneration control.

According to the first embodiment, even when the vehicle speed V islower than or equal to the predetermined vehicle speed V1 where runningnoise during traveling is small, it is possible to mask noise from theelectric oil pump 75 by noise from sources other than the electric oilpump 75 and make the noise from the electric oil pump 75 inconspicuous.

Next, a second embodiment of the present disclosure will be described.In the following description, like reference numerals denote the sameportions as those of the above-described first embodiment, and thedescription thereof is omitted.

In the second embodiment, in the case where the accelerator operationamount Acc falls within the range from the predetermined value X to thepredetermined value Y, the target rotation speed Nop* of the electricoil pump 75 is set to zero. That is, the electric oil pump 75 isstopped. In the case where the accelerator operation amount Acc fallswithin the range from the predetermined value X to the predeterminedvalue Y, a load on the electric motors MG the meshing gears, and thelike, reduces, so noise that occurs from sources other than the electricoil pump 75 reduces. Therefore, when noise suppression is given a higherpriority, it is desirable to stop the electric oil pump 75 in the casewhere the accelerator operation amount Acc falls within the range fromthe predetermined value X to the predetermined value Y. An EOP drivecontrol unit 100 (see FIG. 3) according to the second embodiment causesnoise not to occur by setting the rotation speed Nop of the electric oilpump 75 to zero (by stopping the electric oil pump 75) in the case wherethe accelerator operation amount Acc falls within the range from thepredetermined value X to the predetermined value Y.

FIG. 6 is a flowchart that shows control operations of electroniccontrol units according to the second embodiment of the presentdisclosure and, specifically, a flowchart that illustrates controloperations over the electric oil pump 75.

Initially, in step S1 (hereinafter, step is omitted) corresponding tothe function of the EOP drive control unit 100 in the second embodiment,which corresponds to the EOP drive control unit 84 according to thefirst embodiment, it is determined whether a request to operate theelectric oil pump 75 has been output. When a request to operate theelectric oil pump 75 has not been output, negative determination is madein S1, and the process proceeds to S6. In S1, when a request to operatethe electric oil pump 75 has been output, affirmative determination ismade in S1, and the process proceeds to S2.

In S2 corresponding to the function of the EOP drive control unit 100,it is determined whether the vehicle speed V is lower than or equal tothe predetermined vehicle speed V1. When the vehicle speed V exceeds thepredetermined vehicle speed V1, negative determination is made in S2,and the process proceeds to S5. When the vehicle speed V is lower thanor equal to the predetermined vehicle speed V1, affirmativedetermination is made in S2, and the process proceeds to S3.

In S3 corresponding to the function of the EOP drive control unit 100,it is determined whether the accelerator operation amount Acc fallswithin the range from the predetermined value X to the predeterminedvalue Y. When the accelerator operation amount Acc falls within therange from the predetermined value X to the predetermined value Y,affirmative determination is made in S3, and the process proceeds to S6.In S6 corresponding to the function of the EOP drive control unit 100,the electric oil pump 75 is stopped (the rotation speed is set to zero).Therefore, noise does not occur from the electric oil pump 75. As aresult, the influence of noise from the electric oil pump 75 does notoccur.

Referring back to S3, when the accelerator operation amount Acc fallsoutside the range from the predetermined value X to the predeterminedvalue Y, the process proceeds to S4. In S4 corresponding to the functionof the EOP drive control unit 100, it is determined whether theaccelerator operation amount Acc is smaller than the predetermined valueX. When the accelerator operation amount Acc is smaller than thepredetermined value X, affirmative determination is made in S4, and theprocess proceeds to S8.

In S8 corresponding to the function of the EOP drive control unit 100,it is determined whether the depression force BS on the brake pedal 73is larger than or equal to the threshold F set in advance. When thedepression force BS on the brake pedal 73 is larger than or equal to thethreshold F, affirmative determination is made in S8, and the processproceeds to S9. In S9 corresponding to the function of the EOP drivecontrol unit 100, the target rotation speed Nop* of the electric oilpump 75 is set to the rotation speed C, and the electric oil pump 75 iscontrolled so as to operate at the rotation speed C. When the depressionforce BS on the brake pedal 73 is smaller than the threshold F in S8,negative determination is made in S8, and the process proceeds to S20.In S20 corresponding to the function of the EOP drive control unit 100,the target rotation speed Nop* of the electric oil pump 75 is set to avalue between a rotation speed of zero and the rotation speed C inresponse to the depression force BS on the brake pedal 73, and theelectric oil pump 75 is controlled so as to operate at the set rotationspeed. When the accelerator operation amount Acc exceeds thepredetermined value Y in S4, negative determination is made in S4, andthe process proceeds to S5. In S5 corresponding to the function of theEOP drive control unit 100, the target rotation speed Nop* of theelectric oil pump 75 is set to the rotation speed A, and the electricoil pump 75 is controlled so as to operate at the rotation speed A.

As described above, according to the second embodiment as well, similaradvantageous effects to those of the above-described first embodimentare obtained. In the second embodiment, noise that occurs from theelectric oil pump 75 is eliminated by setting the rotation speed Nop ofthe electric oil pump 75 to zero, that is, stopping the electric oilpump 75, in the case where the accelerator operation amount Acc fallswithin the range from the predetermined value X to the predeterminedvalue Y. Thus, it is possible to reliably reduce a feeling ofstrangeness due to noise from the electric oil pump 75.

Next, a third embodiment of the present disclosure will be described. Inthe above-described first embodiment or second embodiment, in the casewhere the accelerator operation amount Acc falls within the range fromthe predetermined value X to the predetermined value Y, the rotationspeed of the electric oil pump 75 is controlled to the rotation speed Bor the electric oil pump 75 is stopped. In the third embodiment, therotation speed of the electric oil pump 75 is changed depending on theoil temperature Toil in the case where the accelerator operation amountAcc falls within the range from the predetermined value X to thepredetermined value Y.

Since the viscosity of oil is high in a state where the oil temperatureToil is low, it takes time to restart the electric oil pump 75 in astate where the electric oil pump 75 is stopped and supply oil to theelectric motors MG, the meshing gears, and the like. On the other hand,since the viscosity of oil is low in a state where the oil temperatureToil is high, when the electric oil pump 75 is restarted in a statewhere the electric oil pump 75 is stopped, it is possible to quicklysupply oil to the electric motors MG, the meshing gears, and the like.In consideration of this, in the third embodiment, the rotation speed Dof the electric oil pump 75 is changed in response to the oiltemperature Toil in the case where the accelerator operation amount Accfalls within the range from the predetermined value X to thepredetermined value Y.

FIG. 7 shows the relationship between an oil temperature Toil and atarget rotation speed Nop* of the electric oil pump 75 in the case wherethe accelerator operation amount Acc falls within the range from thepredetermined value X to the predetermined value Y. In FIG. 7, theabscissa axis represents the oil temperature Toil, and the ordinate axisrepresents the target rotation speed Nop*.

As shown in FIG. 7, when the oil temperature Toil is lower than or equalto a predetermined oil temperature T1, the target rotation speed Nop* isset to the rotation speed D. The rotation speed D is empirically oranalytically obtained in advance, and is set to a rotation speed atwhich it is possible to quickly supply oil to the electric motors MG,and the like, from a state where the electric oil pump 75 is stopped. Inthe range higher than the predetermined oil temperature T1, as the oiltemperature Toil rises, the target rotation speed Nop* decreases. As theoil temperature Toil reaches a predetermined oil temperature T2, thetarget rotation speed Nop* is set to zero. In this way, the targetrotation speed Nop* varies depending on the oil temperature Toil, andthe target rotation speed Nop* is set to a lower value as the oiltemperature Toil rises. The predetermined oil temperature T2 is anexample of the predetermined oil temperature according to the presentdisclosure.

The predetermined oil temperatures T1, T2 for the oil temperature Toilare empirically or analytically obtained in advance. For example, thepredetermined oil temperature T1 is set to a threshold within the rangein which the electric oil pump 75 needs to be driven at the rotationspeed D in consideration of the viscosity of oil. The predetermined oiltemperature T2 is, for example, set to a value at which it is possibleto supply oil to the electric motors MG, and the like, within apredetermined time at the time when the electric oil pump 75 isrestarted from a state where the electric oil pump 75 is stopped.

As described above, in the case where the accelerator operation amountAcc falls within the range from the predetermined value X to thepredetermined value Y, the target rotation speed Nop* of the electricoil pump 75 may be changed on the basis of the oil temperature Toil ofoil. Even in the case set as described above, similar advantageouseffects to those of the above-described first embodiment or secondembodiment are obtained. By changing the target rotation speed Nop* ofthe electric oil pump 75 in response to the oil temperature Toil, therotation speed Nop of the electric oil pump 75 is set to a furtheroptimal value in response to the oil temperature Toil. Therefore, noisethat occurs from the electric oil pump 75 is made inconspicuous, whileshortage of oil supplied to the electric motors MG, and the like, isprevented.

Next, a fourth embodiment of the present disclosure will be described.In the above-described first to third embodiments, when the acceleratoroperation amount Acc becomes smaller than the predetermined value X,regeneration control over the second electric motor MG2 is executed. Inthe fourth embodiment, when the accelerator operation amount Acc becomeszero, regeneration control over the second electric motor MG2 isexecuted.

FIG. 8 shows the relationship between an accelerator operation amountAcc and a target rotation speed Nop* of the electric oil pump 75according to the fourth embodiment. As shown in FIG. 8, a lower limitthreshold of the range of the accelerator operation amount Acc, in whichthe target rotation speed Nop* of the electric oil pump 75 is set to therotation speed B, is zero. When the accelerator operation amount Acc iszero, the target rotation speed Nop* of the electric oil pump 75 is setto the rotation speed C higher than the rotation speed B. In the fourthembodiment, when the accelerator operation amount Acc becomes zero,regeneration control over the second electric motor MG2 is executed. Inaddition to this, when the accelerator operation amount Acc becomeszero, the rotation speed of the electric oil pump 75 is increased. Thatis, when the accelerator operation amount Acc becomes zero, regenerationcontrol over the second electric motor MG2 is executed, so noise due toregeneration control increases. Therefore, the rotation speed of theelectric oil pump 75 is increased within the range in which noise fromthe electric oil pump 75 is masked by the noise due to the regenerationcontrol.

Through control as described above as well, when the acceleratoroperation amount Acc becomes zero, noise from the second electric motorMG2 increases with regeneration control over the second electric motorMG2. Therefore, even when the rotation speed of the electric oil pump 75is increased, noise that occurs from the electric oil pump 75 is maskedby noise from other sources including the second electric motor MG2 andbecomes inconspicuous. The amount of heat generation also increasesduring regeneration control over the second electric motor MG2. In thissituation, the rotation speed of the electric oil pump 75 is also high,so it is possible to supply the amount of oil required to cool thesecond electric motor MG2. Therefore, according to the fourth embodimentas well, similar advantageous effects to those of the above-describedfirst to third embodiments are obtained.

The embodiments of the present disclosure are described in detail withreference to the accompanying drawings; however, the present disclosureis also applied to another mode.

For example, in each of the above-described embodiments, the vehicledriving system 10 includes the first electric motor MG1, the secondelectric motor MG2, and the planetary gear train 24 that functions as apower distribution mechanism; however, the present disclosure is notalways limited to the vehicle driving system 10. The present disclosureis applicable to a system where appropriate as long as the systemincludes an electric motor that serves as a vehicle driving source andan electric oil pump that supplies oil to the electric motor. Forexample, the present disclosure is also applicable to an electricvehicle that includes no engine.

In each of the above-described embodiments, the rotation speed Nop ofthe electric oil pump 75 is controlled to the rotation speed B that is aconstant value in the case where the accelerator operation amount Accfalls within the range from the predetermined value X to thepredetermined value Y; however, the rotation speed B is not alwayslimited to a constant value. For example, the rotation speed Nop of theelectric oil pump 75 may be changed as needed to a rotation speed thatvaries at a predetermined inclination in proportion to the acceleratoroperation amount Acc.

In the above-described second embodiment, in the case where theaccelerator operation amount Acc falls within the range from thepredetermined value X to the predetermined value Y, the electric oilpump 75 is stopped. Instead, timer control may be executed. For example,the electric oil pump 75 is driven at the rotation speed B when apredetermined time has elapsed from the time at which the electric oilpump 75 is stopped.

In the above-described third embodiment, in the case where theaccelerator operation amount Acc falls within the range from thepredetermined value X to the predetermined value Y, the rotation speedNop of the electric oil pump 75 is changed in response to the oiltemperature Toil. Instead, in the case where the accelerator operationamount Acc is smaller than the predetermined value X or exceeds thepredetermined value Y as well, the rotation speed Nop of the electricoil pump 75 may be changed in response to the oil temperature Toil.

In each of the above-described embodiments, the rotation speed Nop ofthe electric oil pump 75 in the case where the vehicle speed V exceedsthe predetermined vehicle speed V1 and the rotation speed Nop of theelectric oil pump 75 in the case where the accelerator operation amountAcc exceeds the predetermined value Y both are set to the rotation speedA. Instead, these values do not need to be the same, and may be set todifferent values.

In each of the above-described embodiments, the target rotation speedNop* of the electric oil pump 75 is varied between the case where theaccelerator operation amount Acc is smaller than the predetermined valueX and the case where the accelerator operation amount Acc exceeds thepredetermined value Y. Instead, these target rotation speeds Nop* may beset to the same rotation speed. In this case, in the above-describedflowcharts, step of determining whether the accelerator operation amountAcc is smaller than the predetermined value X is not required, so a loadon the electronic control unit 50 is reduced.

In each of the above-described embodiments, the target rotation speedNop* that is set in the case where the accelerator operation amount Accis smaller than the predetermined value X is set to the rotation speedC, the target rotation speed Nop* that is set in the case where theaccelerator operation amount Acc exceeds the predetermined value Y isset to the rotation speed A, and the rotation speed A is higher than therotation speed C; however, the target rotation speed Nop* is not alwayslimited to such settings. That is, the rotation speed C may be set to avalue higher than the rotation speed A.

In each of the above-described embodiments, the mechanical oil pump 30is not driven during operation of the electric oil pump 75. Instead, themechanical oil pump 30 that is driven by the engine 12 may be drivenduring operation of the electric oil pump 75. In this case, non-EOPnoise shown in FIG. 4, including noise from the engine 12, isconsidered.

The above-described embodiments are only illustrative. The presentdisclosure may be implemented in a mode including various modificationsor improvements on the basis of the knowledge of persons skilled in theart.

What is claimed is:
 1. A driving system for a vehicle, the drivingsystem comprising: an electric motor configured to function as a drivingsource of the vehicle; an electric oil pump configured to supply oil toa cooling and lubrication required portion including the electric motor;and an oil pump controller configured to (i) supply oil to the coolingand lubrication required portion by driving the electric oil pump whilethe vehicle is traveling, and (ii) control a rotation speed of theelectric oil pump when an accelerator operation amount of the vehiclefalls within a predetermined range to a rotation speed lower than arotation speed of the electric oil pump when the accelerator operationamount falls outside the predetermined range.
 2. The driving systemaccording to claim 1, wherein the oil pump controller is configured toset a lower limit threshold of the predetermined range of theaccelerator operation amount to a value at which regeneration controlover the electric motor is started.
 3. The driving system according toclaim 2, wherein the oil pump controller is configured to set the lowerlimit threshold of the predetermined range to zero.
 4. The drivingsystem according to claim 3, wherein the oil pump controller isconfigured to change the rotation speed of the electric oil pump on thebasis of whether a depression force on a brake pedal is larger than orequal to a threshold set in advance.
 5. The driving system according toclaim 1, wherein the oil pump controller is configured to control therotation speed of the electric oil pump to zero, when the acceleratoroperation amount falls within the predetermined range.
 6. The drivingsystem according to claim 5, wherein the oil pump controller isconfigured to control the rotation speed of the electric oil pump tozero, when an oil temperature of oil is higher than or equal to apredetermined oil temperature.
 7. The driving system according to claim1, wherein the oil pump controller is configured to control the rotationspeed of the electric oil pump when the accelerator operation amountfalls within the predetermined range to a rotation speed lower than therotation speed of the electric oil pump when the accelerator operationamount falls outside the predetermined range, when a vehicle speedbecomes lower than or equal to a predetermined vehicle speed set inadvance.